Re: [PATCH] x86/retpoline/entry: Disable the entire SYSCALL64 fast path with retpolines on

[Andy Lutomirski]

On Fri, Jan 26, 2018 at 10:54 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, Jan 26, 2018 at 10:23 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
>>
>> The issue is that doing it this way gives us, effectively:
>>
>> long sys_foo(int a, int b)
>> {
>>   body here;
>> }
>>
>> long SyS_foo(const struct pt_regs *regs)
>> {
>>   return sys_foo(regs->di, regs->si);
>> }
>>
>> whereas what we want is *static* long sys_foo(...).
>
> How about just marking 'sys_foo()' as being always_inline (but still
> not static)? Because the case that _matters_ is that SyS_foo(), thing
> when this is enabled.
>
> Sure, you'll get two copies of the code (one in SyS_foo(), the other
> being the callable-from C 'sys_foo()' that is exported and almost
> never used). But that seems a fairly small price to pay. We could
> leave it for later to try to get rid of the unused copies entirely.
>

I could do that, but Josh Triplett will yell at me.

Anyway, I'll fiddle with it.  This isn't exactly high priority.